The present invention relates generally to rotary heat exchangers and, more specifically, to bypass seals for sealing the gaps around the exchange baskets.
A rotary regenerative heat exchanger is employed to transfer heat from one hot gas stream, such as a flue gas stream, to another cold gas stream, such as combustion air. The rotor contains a mass of heat absorbent material which is first positioned in a passageway for the hot gas stream where heat is absorbed by the heat absorbent material. As the rotor turns, the heated absorbent material enters the passageway for the cold gas stream where the heat is transferred from the absorbent material to the cold gas stream.
In a typical rotary heat exchanger, such as a rotary regenerative air preheater, the cylindrical rotor is disposed on a central rotor post and divided into a plurality of sector-shaped compartments by a plurality of radial partitions, known as diaphragms, extending from the rotor post to the outer peripheral shell of the rotor. These sector shaped compartments are loaded with modular heat exchange baskets which contain the mass of heat absorbent material commonly comprised of stacked plate-like elements.
The rotor is surrounded by a housing and the ends of the rotor are partially covered by sector plates located between the gas inlet and outlet ducts which divide the housing into hot gas and cold gas sides. In order to improve the efficiency of operation, it is conventional to provide seals, which are referred to as radial seals, on the ends of the rotor such that the seals will come into proximity with the sector plates and minimize the flow of gases between the hot and cold sides at the ends of the rotor. These seals are attached to the top and bottom edges of the diaphragms.
The conventional modular heat exchange basket comprises a frame which is open on each end and which may or may not have solid side walls. These baskets are loaded axially into the rotor from the ends and stay plates are located between and support radially adjacent baskets. To ensure that the baskets can be freely inserted, it is necessary to have the baskets undersized as compared to the compartments formed by the diaphragms and stay plates so that there is a clearance. Therefore, gaps exist between the sides of the baskets and the diaphragms which permit a portion of the gas streams to bypass the heat exchange surface in the baskets. The present method of sealing the bypass gap is to weld bars of a proper width to the diaphragm so that they contact the basket and fill the gap. This method, in addition to being time consuming and expensive, still allows some leakage to occur due to irregularities in the basket alignment and the fact that the diaphragm may not be exactly flat.